1. Technical Field
The present invention relates to an image display device and an image display method in which an image is displayed by driving a light source so as to reduce uneven luminance or uneven color.
2. Description of Related Art
A liquid crystal display device displays an image by allowing a liquid crystal panel to transmit or block light emitted from a backlight. The color reproducibility, the contrast performance and the power consumption of the liquid crystal display device mainly depend upon the performance or control of the liquid crystal panel and the backlight. Recently, a driving method in which a backlight is divided into a plurality of areas for controlling an emission ratio in each area (hereinafter referred to as the area active drive) has been proposed.
In the area active drive, when a part of an image to be displayed has low luminance, the emission ratio of an area of the backlight corresponding to this part is lowered so as to set the transmittance of the liquid crystal panel in accordance with the emission ratio. Since the emission ratio of each area of the backlight may be thus optimized, the power consumption of the backlight as a whole may be reduced. Furthermore, since the emission ratio is lowered in every area, a black floating in liquid crystal display (for example, a state where a black portion on a screen is displayed slightly bright when the lighting is off) may be reduced, and in addition, the contrast and the image quality may be improved.
In this area active drive, an RGB-LED light source including LEDs (light emitting diodes) of three colors of red (R), green (G) and blue (B) may be used as the backlight. In this case, it is necessary not only to increase/decrease the emission ratio of every area but also to control each of the three color LEDs in the area. Specifically, when a displayed image corresponding to a given area is in blue alone, the red (R) LED (hereinafter referred to as the R-LED) and the green (G) LED (hereinafter referred to as the G-LED) are placed in an off state and the blue (B) LED (hereinafter referred to as the B-LED) alone is placed in an on state in this area, and the transmittance of the liquid crystal display panel is set in accordance with the emission ratio of the B-LED. Thus, an image with a high color purity of blue alone may be displayed. Since a necessary LED alone out of all the LEDs present in every area is controlled in this manner, the effect to reduce the power consumption may be highly attained as compared with the case where a white light source is used. Furthermore, since the color purity of each primary color is increased, the color gamut of a displayed image may be increased.
With respect to the aforementioned area active drive, Japanese Patent Application Laid-Open No. 2005-338857 describes a device and a method in which a backlight may be locally controlled in luminance and color characteristics. In the device and the method described in Japanese Patent Application Laid-Open No. 2005-338857, a liquid crystal display panel is divided into a plurality of areas, and the backlight includes a plurality of LEDs for emitting light to the respective areas. The emission ratio of each LED is controlled in accordance with a peak value of the gradation values of each area of the liquid crystal panel.